lab 2

Qualitative Cation Tests

Michele Hopkins

General Chemistry II/ CHEM-182-DL1

Professor Amal Bassa

July 20, 2014

Introduction

Procedure

1. I consecutively testing the identified anions, as well as I performed the same tests on the unknown

solution to conclusively determine its identity.

2. In the first test tube I placed 8 drops of the anion. Than added drops of hydrochloric acid to the anion solution

3. In the second test tube I put 8 drops of the anion solution and added 3 drops of silver nitrate solution. (noted reactions)

4. By adding a few drops of nitric acid, I acidify the test tube. I mixed well and noted if the precipitate remains.

5. In the third test tube I tested for this anion by warming a chemical place the test

tube containing the chemical into a 50-mL beaker of hot tap water for a few minutes.

6. Bromide (Br-) and Iodide (I-): (I took fresh chlorine water by combining in a graduated

cylinder approximately 1ml of bleach, 5ml of tap water, and 6 drops of HCl and stirred.

7. I ledabel an empty pipet and sucked up this chlorine solution.

8. Add 10 drops of the test solution add 2 to 3 drops of the organic reagent (hexanes or similar) and several drops

of chlorine water.

9. Carbonate (CO32-): Acidify 20 drops of the solution with 2 drops of HCl. Carbonates produce

an odorless gas (CO2) which should produce a precipitate when bubbled through a saturated

calcium hydroxide solution.

10. Chloride (Cl-): To 6 drops of the test solution add 2 drops of AgN03, silver nitrate solution.

A white precipitate that dissolves readily when the solution is made definitely basic with

aqueous ammonium indicates the presence of the chloride ion.

11. Phosphate (PO4 3-): Acidify 10 drops of the test solution with 1 drop of HNO3, nitric acid, and

added 7 drops of ammonium molybdate solution.

12. Sulfate (SO4 2-): To 10 drops of the test solution add 5 drops of the BaCl2, barium chloride

solution. A white precipitate that is insoluble in HCl indicates the presence of sulfate.

13. Sulfide (S2-): Acidify 10 drops of the test solution with HCl. The odor of hydrogen sulfide (H2S)

should be apparent (it smells like rotten eggs!). I warmed the solution and then held

a small piece of moist lead acetate paper at the mouth of the test tube. If the paper turns

black (caused by PbS) this indicates the presence of sulfide.

Qualitative Cation Tests

Peter Jeschofnig, Ph.D. Version 42-0194-00-01

Lab Report Assistant

This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate students’ writing of lab reports by providing this information in an editable file which can be sent to an instructor.

Observations

Data Table: Qualitative Cation Tests
Name	Test Tube 1 (HCl)	NH3	Test Tube 2 (NaOH)	Excess
Aluminum 3+	No reaction	n/a	White ppt.	Ppt. dissolves
Ammonium +	Gas (fumes)/clear	n/a	No reaction	n/a
Calcium 2+	n/a	n/a	Faint, white ppt. which has appreciable solubility in water.	Ppt. is insoluble
Copper 2+	n/a	n/a	Blue ppt.	Ppt. is insoluble
Iron 3+	n/a	n/a	Reddish brown ppt.	Ppt. is insoluble
Lead 2+	White ppt.	Ppt. is insoluble	White ppt.	Ppt. dissolves
Silver +	White ppt.	Ppt. dissolves	Brown ppt.	Ppt. is insoluble
Zinc 2+	n/a	n/a	White gelatinous ppt.	Ppt. dissolves

Name	Test Tube 3 (NH3)	Excess	Test Tube 4 confirmation
Aluminum 3+	Cloudy white ppt.	Ppt. is insoluble	pink/reddish when aluminon reagent and ammonium acetate added . No change when made alkaline.
Ammonium +	No reaction	n/a	Red litmus paper turned blue/ ammonia fumes evident.
Calcium 2+	Faint, white ppt. which has appreciable solubility in water	Ppt. is insoluble	Add a few drops of Ammonium Oxalate solution--- a white ppt. forms.
Copper 2+	Blue ppt.	Ppt. dissolves	Acidify with one drop of HCl(6M) and add one drop of Potassium Hexacyanoferrate (II) solution ---- red brown ppt.
Iron 3+	Reddish brown ppt.	Ppt. is insoluble	Add a few drops of Potassium Hexacyanoferrate (II) solution --- an intense blue ppt. forms.
Lead 2+	White ppt.	Ppt. is insoluble	Add a few drops of potassium chromate(1M K2CrO4) --- Yellow ppt. PbCrO4
Silver +	Brown ppt.	Ppt. dissolves	Add HCl, until a ppt. forms. Ppt. dissolves in aq. NH3. Ppt. reappears on addition of HNO3.
Zinc 2+	White ppt.	Ppt. dissolves	Add excess Sodium Hydroxide(2M) solution. Then add a few drops of Sodium Sulphide solution (0.2M)--- a white ppt.

Questions

A. Write net ionic equations for all reactions that produce a precipitate.

Ag+(aq.) + Cl-(aq.) ----( AgCl (s)

2 Ag+(aq.)+ 2OH- ---( Ag2O (s) + H2O(l)

Pb2+(aq.)+2Cl- (aq.) ----( PbCl2(s)

Pb2+(aq.)+2OH-(aq.) ----(Pb(OH)2 (s)

Cu2+(aq.) +2OH-(aq.) ----( Cu(OH)2 (s)

2Cu2+(aq.)+SO42- (aq.) +2NH3(aq.)+2 H2O(l) -----( Cu(OH)2.CuSO4(s) +2NH4+ (aq.)

2Cu2+(aq.)+[Fe(CN)6]4- (aq.) -----(Cu2[Fe(CN)6] (s)

Zn2+ (aq.)+ 2OH- (aq.) ----( Zn(OH)2 (s)

Zn2+ (aq.)+2NH3(aq.)+ H2O(l) ---( Ag2O (s)+ 2NH4+ (aq.)

Zn2+(aq.) + S2-(aq) -----( ZnS(s)

Fe3+ (aq.)+ 3OH- (aq.) ----( Fe(OH)3(s)

4Fe3+ (aq.)+3[Fe(CN)6]4- (aq.) ----(Fe4[Fe(CN)6]3 (s)

Ca2+(aq) + ( COO)22-(aq) -----( Ca(COO)2 (s)

B. Identify the cations that precipitate with hydrochloric acid and dissolve in the presence of ammonia. The cations that precipitate with hydrochloric acid and dissolve in the presence of ammonia is

C. Identify the cations that precipitate with hydrochloric acid and do not redissolve in the presence of ammonia. The cations that precipitate with hydrochloric acid and do not redissolve in the presence of ammonia is

D. Identify the cations that precipitate upon addition of two or three drops of sodium hydroxide but redissolve upon addition of excess sodium hydroxide. The cations that precipitate upon addition of two or three drops of sodium hydroxide but redissolve upon addition of excess sodium hydroxide is Al NO3)3 and Zn(NO3)3

E. Identify the cations that precipitate upon addition of two or three drops of sodium hydroxide and are not affected by additional sodium hydroxide. The cations that precipitate upon addition of two or three drops of sodium hydroxide and are not affected by additional sodium hydroxide is Ca(NO3)2 and Cu(NO3)3

F. Identify the cations that precipitate upon addition of two or three drops of aqueous ammonia but redissolve upon addition of excess aqueous ammonia. The cations that precipitate upon addition of two or three drops of aqueous ammonia but redissolve upon addition of excess aqueous ammonia is

G. Identify the cations that precipitate upon addition of two or three drops of aqueous ammonia and are not affected by additional aqueous ammonia. The cations that precipitate upon addition of two or three drops of aqueous ammonia and are not affected by additional aqueous ammonia is

H. What simple test would distinguish Ag+ and Cu2+ ? Simply add HCI silver will precipitate and copper will not.

Conclusion

Reference

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